As an internal combustion engine including plural groups of cylinders (banks) connected to different exhaust gas passages, there is known a V-type engine in which plural groups of cylinders are connected to different exhaust gas passages, respectively, for example. The internal combustion engine of this kind includes a catalyst and a filter for purifying exhaust gas in each of the exhaust gas passages.
For example, Japanese Patent Application Laid-open under No. 11-117786 (Reference-1) discloses a technique, in which a SOx catalyst is provided for each exhaust gas passage connected to each bank and an air-fuel ratio is individually controlled for each bank so that the temperature of the SOx catalyst becomes a regenerating temperature at which the catalyst can be regenerated (activated). Thereby, regeneration control is executed. In addition, Japanese Patent Application Laid-open under No. 2004-52641 (Reference-2) discloses a technique in which, in the V-type engine, the regeneration control of the catalysts is executed after a temperature difference between the catalysts provided in the exhaust gas passages of the respective banks becomes zero. Moreover, Japanese Patent Application Laid-open under No. 2004-339973 (Reference-3) discloses a technique in which, in the V-type engine, a timing of regenerating the catalyst is estimated for each bank, and the regeneration control is executed for each bank.
By the way, the states of the catalysts in the banks do not completely coincide with each other, and hence the regeneration control of the catalysts to be executed may be different between the banks. In this case, the regeneration of the catalysts can be more effectively executed by a method of executing the regeneration control at different timings for each bank as compared with a method of simultaneously executing the regeneration control to the entire banks. However, when the combustion mode is changed before and after the execution of the regeneration control, e.g., when the present combustion mode has to be changed for the purpose of executing the regeneration control, it is not preferable that the regeneration control is executed at the different timings for each bank. For example, if the combustion modes of the banks are changed differently for the purpose of the regeneration control and the regeneration control is executed at the different timings, fuel consumption of the internal combustion engine and drivability may be significantly deteriorated.
However, in the exhaust gas purifying apparatuses according to the above-mentioned Reference-1 to Reference-3, since the regeneration control is independently executed for each bank even when the combustion mode is changed before and after the execution of the regeneration control, the drivability may be deteriorated.